Method of making helical packing rings



April 4, 1939. M. G. KURTH' 2,152,393

METHOD OF MAKING BELICAL PACKING RINGS Filed Oct. 2, 1955 Gttorneg;

Patented Apr. 4, 1939 PATENT oFFIcE METHOD OF MAKING HELICAL PACKING RINGS Matthew G. Kurth, Madison, Wis.

Application October 2, 1935, Serial No. 43,183

1 Claim.

This invention relates to improvements in helical packing rings, and the art of manufacturing the same.

The present invention has for its primary objects the simplification of production of toothed helical packing rings.

More specifically, the present invention seeks to improve the cutting operation by first grooving helically a cylindrical metal tube section (either internally or externally) and thereafter removing such ungrooved surface portions as are necessary to intersect the groove and to free the coils of the helical piston ring, and to produce the required bearing surface.

disclosed will be apparent to those skilled in the art upon a study of the following specification and claim.

In the drawing:

Figure 1 is a side elevation partly in fragmentary cross section through a piston assembly showing packing made in accordance with my invention.

Figure 2 is a fragmentary view in side eleva- 35 tion of the tailstock of a milling machine, showing an internally threaded helix in diagrammatic cross section in the process of manufacture.

Figure 3 is a fragmentary view in side elevation, partly in cross section, showing an externally threaded helix in the process of manufacture.

Like parts are identified by the same reference characters throughout the several views.

I shall first describe a piston and packing ring assembly illustrating a type of rings for which the present manufacturing process is adapted.

The piston 5 has a packing groove at 6 sufficiently deep in a radial direction and sufficiently elongated in an axial direction to receive compound packing comprising the helices 1 and 8, and a convoluted compression ring 9 which acts on helix 1 in an axial direction.

Each of the helices 1 and 8 is peripherally threaded, helix 1 having a thread Ill throughout its inner periphery and helix 8 having a complementary thread ll throughout its outer periphery, the arrangement being such that the respective threads I0 and. H are inter-engaged in the manner clearly shown in Fig. 1 and claimed in a companionapplication. The terminal coils of each helix will preferably be built up as shown at 12 in Fig. l, and will be tapered toward their extremities as shown at l3, so that each helix will 1;) Further advantages of the invention herein be cylindrical in form with planiform end surfaces to which the axis of the helix is normal.

Each of the helices will also preferably be anchored at its upper end. The terminal portion [3 of the end coil of helix 1 may be secured 5 by a pin [4 driven through the piston head, while the end coil of helix 8 is held by a similar pin [5. A radial pin as shown at l6 may also be used if desired.

The helix 8, having a cylindrical inner surface 10 fitted closely to the piston, will be relatively fixed thereon Whereas the helix 1, being anchored only at its end, will tend to expand and contract both radially and axially. An axial pressure will tend to cause the coils of helix 1 to feed about the 15 threads, joining it with helix 8 to reduce very slightly its axial length and produce a corresponding increase in its diameter. It is the function of the convoluted spring 9 to act on helix 1 to expand its diameter into contact with 20 the cylinder in which piston 5 is made to operate. As the helix 1 expands due to heat, it obviously is incapable of increase in diameter, being confined within the cylinder, and accordingly the excess material is accommodated by 25 a change in length against the compression of spring 9.

In ordinary manufacturing methods the machining of the helices 1 and 8 with their threads I0 and II might afford considerable difiiculty and expense, In accordance with the present invention, however, a cylindrical blank 20 is mounted in a jig 2| on the tailstock screw 22 of a lathe or milling machine on which the 3 internally threaded helix is to be produced. For the production of an externally threaded helix the jig 23 is employed, and similarly mounted to receive blank 24.

Employing a thread. cutting milling tool 25, 4 the blank 20 is helically cut as shown in Fig. 2 to provide the interthread channel 26 and a deeper groove at 21, thus forming the thread H and at the same time almost severing the successive coils of the helix. On the completion 45 of this helical grooving operation performed on the interior of the blank 25, the blank is placed in a lathe and its outer periphery is cut away to a cylindrical form sufiiciently small in diameter so that the helical groove 27 intercepts the 50 cylindrical diameter at all points, thus freeing the coils of the helix from each other and leaving the packing element complete so far as its intermediate helical coils are concerned. The ends will have been left tobe finished separately by 55 ordinary machining operations to produce the parts I2 and I3 as shown in Fig. 1.

The externally threaded helix is similarly produced as shown in Fig. 3, a similar cutter 25 being used on the exterior of the blank 24 to out a channel 250, and a deeper groove 27!] constituting a mechanical converse of channel 26 in groove 21. Upon the completion of the helical milling of the channel 260 and groove 21B throughout the intermediate portion of blank 24, the blank is placed in an ordinary turning lathe and its interior periphery is turned to cut away the metal to an enlarged diameter sufficient so that its cylindrical inner surface intersects at all points the groove 2'10 to free the coils of the helix 8.

If the helix were first completed and thereafter machined to provide the threads on its surface, the operation would be very much more difficult. By the present method any desired aisase's form of complementary threads may be produced at will by simply selecting a milling cutter 25 of suitable contour. I have shown only threads of square cross section, but it will be apparent that other threads, some of which are shown in my companion applications, may readily be provided.

I claim:

The process of making a helical threaded packing element, which process includes the cutting of a relatively wide groove in a tubular blank to provide a helical thread thereon, the cutting of a groove narrower than the first mentioned groove and in the bottom thereof between successive turns of the thread formed on said blank, and the peripheral machining of the blank to intersect the narrower groove, whereby to free the coils of a helix on which such thread is carried. 

